Etchant formulation for selectively removing thin films in the presence of copper, tin, and lead

ABSTRACT

The invention relates to a ball-limiting metallurgy (BLM) etching system and process. The BLM stack is provided for an electrical device that contains an aluminum layer disposed upon a metal first layer. A metal upper layer is disposed above the metal second layer, and an alternative metal third layer is disposed between the metal second layer and the metal upper layer. The etching system and process utilizes an etching solution that includes a nitrogen-containing heterocyclic compound, an ammonium hydroxide compound, an oxidizer, and a metal halide compound. Etching conditions prevent any metallization that is dissolved from redepositing, thus avoiding lowered yields.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] An embodiment of the present invention relates generally tointegrated circuit fabrication. More particularly, an embodiment of thepresent invention relates to electrical connection technology. Inparticular, an embodiment of the present invention relates to etching aball-limiting metallurgy in the presence of lead, tin, and copper.

[0003] 2. Description of Related Art

[0004] Electrical bump connectors such as metal bumps or balls are usedin flip-chip (C4) applications. As the progress of miniaturizationcontinues, the junction between a microelectronic device metallizationand the electrical bump becomes increasingly large relative to the massof the electrical bump. Consequently, junction disparities have anincreasingly detrimental effect on electrical communication between thedevice and the electrical bump.

[0005] Etching of the metal layer or layers exposes a portion of themetallization pads and often leaves residual titanium on the passivationlayer. Etching also mobilizes portions of the metallization pads andredeposits them on the passivation layer. The redeposited metallizationpad material and the residual titanium may form stringers or otherstructures that may lead to electrical test (e-test) failures or fieldfailures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] In order that the manner in which embodiments of the presentinvention are obtained, a more particular description of the inventionbriefly described above will be rendered by reference to specificembodiments thereof which are illustrated in the appended drawings.Understanding that these drawings depict only typical embodiments of theinvention that are not necessarily drawn to scale and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

[0007]FIG. 1 is an elevational cross-section of a semiconductorstructure that reveals metallization according to an embodiment of theinvention;

[0008]FIG. 2 is an elevational cross-section of the semiconductorstructure depicted in FIG. 1 after patterning of a passivation layer;

[0009]FIG. 3 is an elevational cross-section of the semiconductorstructure depicted in FIG. 2 after further processing;

[0010]FIG. 4 is an elevational cross-section of the semiconductorstructure depicted in FIG. 3 after further processing;

[0011]FIG. 5 is an elevational cross-section of the semiconductorstructure depicted in FIG. 4 after further processing;

[0012]FIG. 6 is an elevational cross-section of the semiconductorstructure depicted in FIG. 5 after further processing; and

[0013]FIG. 7 is a chart that describes a process flow embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention relates to an etch process flow and anetching solution that etches a ball-limiting metallurgy (BLM) stack. Inone embodiment, an etch recipe including n-methyl pyrrolidone (NMP),tetra methyl ammonium hydroxide (TMAH), hydrogen peroxide (H₂O₂), andpotassium fluoride (KF). The etch recipe is selective to the lead-tinbumps and the copper pads.

[0015] The following description includes terms, such as upper, lower,first, second, etc. that are used for descriptive purposes only and arenot to be construed as limiting. The embodiments of an apparatus orarticle of the present invention described herein can be manufactured,used, or shipped in a number of positions and orientations.

[0016] Reference will now be made to the drawings wherein likestructures will be provided with like reference designations. In orderto show the structures of embodiments of the present invention mostclearly, the drawings included herein are diagrammatic representationsof integrated circuit structures. Thus, the actual appearance of thefabricated structures, for example in a photomicrograph, may appeardifferent while still incorporating the essential structures ofembodiments of the present invention. Moreover, the drawings show onlythe structures necessary to understand embodiments of the presentinvention. Additional structures known in the art have not been includedto maintain the clarity of the drawings.

[0017]FIG. 1 is a cross-section of a semiconductor structure 10 duringfabrication that includes a substrate 12 and metallization 14 such ascopper pads that make connection to what is commonly referred to asmetal six (M6) by way of non-limiting example. Metallization 14 may bedisposed with an upper surface 16 that is coplanar with substrate 12where substrate 12 may be an interlayer dielectric (ILD) composition. Anitride layer 18 and a passivation layer 20 are formed over substrate 12and metallization 14. Nitride layer 18 and passivation layer 20 act toprotect substrate 12 and to expose metallization 14 according to thepatterning. Passivation layer 20 may be a polyimide material or it maybe an inorganic material such as a silicon oxide that is formed by thedecomposition of tetraethyl ortho silicate (TEOS). Patterning isaccomplished by a first mask (not pictured) that exposes passivationlayer 20.

[0018]FIG. 2 illustrates a patterned passivation structure, thatincludes portions of nitride layer 18 and passivation layer 20, and thatexposes a portion of metallization 14. The process may be carried out byblanket forming nitride layer 18 and passivation layer 20, patterning,etching recess 22, and curing passivation layer 20 where passivationlayer 20 is a polyimide. In one embodiment after the cure, passivationlayer 20 has formed a slope 24 that has an angle, in a range from about30° to about 60°. In one embodiment after the cure, passivation layer 20has formed slope 24 that is about 45°.

[0019]FIG. 3 illustrates further processing that is carried out wherepassivation layer 20 and metallization 14 are covered with a metal firstlayer 26 a metal second layer 28, a metal third layer 30, and a metalupper layer 32. In one embodiment, metal first layer 26 is a refractorymetal such as titanium, zirconium, hafnium, and the like. Otherrefractory metals for metal first layer 26 include nickel, cobalt,palladium, platinum, and the like. Other refractory metals for metalfirst layer 26 include chromium, molybdenum, tungsten, and the like.Other refractory metals for metal first layer 26 include scandium,yttrium, lanthanum, cerium, and the like. One property embodiment is ametal first layer 26 that exhibits sufficient adhesion to themetallization that liftoff or spalling thereof will not occur duringfabrication, test, and ordinary field use.

[0020] In one embodiment, metal first layer 26 is titanium that isformed by physical vapor deposition (PVD) to a thickness in a range fromabout 500 Å to about 2,000 Å. In another embodiment, metal first layer26 is PVD titanium that is formed to a thickness of about 1,000 Å. Inanother embodiment, metal first layer 26 is chromium that is formed byPVD to a thickness in a range from about 500 Å to about 2,000 Å. Inanother embodiment, metal first layer is PVD chromium that is formed toa thickness of about 1,000 Å.

[0021] Metal second layer 28 is formed by PVD according to knowntechnique. In one embodiment, metal second layer 28 has a thickness in arange from about 500 Å to about 4,000 Å. In one embodiment, metal secondlayer 28 has a thickness in a range from about 750 Å to about 2,000 Å.In one embodiment, metal second layer 28 has a thickness of about 1,000Å. In one embodiment, metal second layer 28 is Al and the like. Inanother embodiment, metal second layer 28 is selected from Ti, doped Ti,TiW, and the like. In another embodiment, metal second layer 28 isselected from Zr, Hf, and the like. Metal second layer 28 acts as a tindiffusion barrier and thermo-mechanical buffer layer.

[0022] Metal second layer 28 is covered with metal third layer 30 thatis substantially the same metal as metal first layer 26. In oneembodiment, metal third layer 30 is formed by PVD according to knowntechnique. In one embodiment, metal third layer 30 is substantially thesame composition as metal first layer 26, within usual processvariations. Alternatively, metal third layer 30 is substantially thesame metal type as metal first layer 26 according to grouping as setforth herein. Accordingly, “substantially the same metal” or“substantially the same composition” may be referred to as substantiallythe same metal type according to grouping as set forth herein.

[0023] In one embodiment, metal first and third layers 26, 30 are Ti,and metal upper layer 32 is NiV. Sputtering of the metal layers 26-32may be carried out under sputtering conditions that will cause them, orone or more of them, to carry a compressive stress that will resistliftoff from passivation layer 24 Such processing conditions are knownin the art.

[0024]FIG. 3 also illustrates further processing in which metal upperlayer 32 is formed over metal second layer 28. In one embodiment, metalupper layer 32 is a refractory metal, a refractory metal alloy, or adoped refractory metal. The refractory metal alloy or the doped metal isin stoichiometric or solid solution ratios. In one embodiment, metalupper layer 32 is a vanadium-alloyed or vanadium-doped metal of at leastone metal selected from nickel, cobalt, palladium, platinum, and thelike. The vanadium may be added where the metal may be ferroelectric. Inone embodiment, metal upper layer 32 is a metal, a vanadium-alloyed, orvanadium-doped metal of at least one selected from titanium, zirconium,hafnium, and the like. In another embodiment, metal upper layer 32 is ametal, a vanadium-alloyed, or vanadium-doped metal of at least oneselected from chromium, molybdenum, tungsten, and the like. In anotherembodiment, metal upper layer 32 is a metal, a vanadium-alloyed, orvanadium-doped metal of at least one selected from scandium, yttrium,lanthanum, cerium, and the like.

[0025] In one embodiment, metal upper layer 32 is a refractory metal, arefractory metal-vanadium alloy, or vanadium-doped metal that is formedby PVD to a thickness in a range from about 1,000 Å to about 4,000 Å. Inanother embodiment, metal upper layer 32 is formed by PVD to a thicknessof about 2,000 Å. In one embodiment, metal upper layer 32 is a NiValloy. In another embodiment, metal upper layer 32 is a vanadium-dopednickel layer.

[0026] Although sputtering of the metal layers 26-32 is a process flowembodiment, evaporation deposition of a composition such as anorganometallic material is also used as a process flow embodiment asknown in the art.

[0027] In an alternative embodiment, metal upper layer 32, is nitridedto form a nitrided metal alloy or a nitrided vanadium-doped metal as setforth herein. Nitriding conditions may be carried out according to knowntechnique for nitridation of metals. In selected embodiments, metalupper layer 32 is a nitrided refractory metal-vanadium alloy or anitrided, vanadium-doped refractory metal. In other selectedembodiments, metal upper layer 32 is a nitrided NiV alloy or a nitridedvanadium-doped nickel metal.

[0028] In another embodiment, metal first and third layers 26, 30, havethicknesses in arbitrary units in a range from about 500 to about 2,000,preferably about 1,000. Similarly, metal second layer 28 has a thicknessin arbitrary units in a range from about 500 to about 4,000, preferablyfrom about 750 to about 2,000, and more preferably about 1,000. Further,metal upper layer 32 has a thickness in a range from about 500 to about6,000, preferably from about 1,000 to about 5,000. As miniaturizationtechnology progresses the ratios of the metal layers may be formedaccording to these proportionalities.

[0029] One metal stack embodiment includes metal first layer 26 of Ti atabout 1,000 Å, metal second layer 28 of Al at about 1,000 Å, metal thirdlayer 30 of Ti at about 1,000 Å, and metal upper layer 32 of nitridedNiV at about 4,000 Å. Another metal stack embodiment includes metalfirst layer 26 of Ti at about 500 Å, metal second layer 28 of Al atabout 1,000 Å, metal third layer 30 of Ti at about 500 Å, and metalupper layer 32 of nitrided NiV at about 2,000 Å.

[0030] Another metal stack embodiment includes metal first layer 26 ofTi at about 1,000 Å, metal second layer 28 selected from doped Ti, Ti,and TiW at about 1,000 Å, metal third layer 30 of Ti at about 1,000 Å,and metal upper layer 32 of nitrided NiV at about 4,000 Å. Another metalstack embodiment includes metal first layer 26 of Ti at about 500 Å,metal second layer 28 selected from doped Ti, Ti, and TiW at about 1,000Å, metal third layer 30 of Ti at about 500 Å, and metal upper layer 32of nitrided NiV at about 2,000 Å.

[0031] Another metal stack embodiment includes metal first layer 26 ofTi at about 1,000 Å, metal second layer 28 selected from Zr and Hf atabout 1,000 Å, metal third layer 30 of Ti at about 1,000 Å, and metalupper layer 32 of nitrided NiV at about 4,000 Å. Another metal stackembodiment includes metal first layer 26 of Ti at about 500 Å, metalsecond layer 28 selected from Zr and Hf, and TiW at about 1,000 Å, metalthird layer 30 of Ti at about 500 Å, and metal upper layer 32 ofnitrided NiV at about 2,000 Å.

[0032] In an alternative embodiment, metal third layer 30 is omitted.Consequently, the BLM stack includes metal first layer 26, metal secondlayer 28 and metal upper layer 32 with the various compositional andthickness embodiments as set forth herein.

[0033] Following the formation of the metal layers 26-32 as set forthherein, processing may continue by plating a bump precursor over thefour-metal-layer stack similar to semiconductor structure 10 depicted inFIG. 4 according to various process flow embodiments. Further processingas set forth herein may result in a solder ball (not pictured). Becausesome intermetallic material may form between the solder ball andmetallization 14, the metal layers 26-32 act to prevent excessiveintermetallic formation, and to resist tin migration towardmetallization 14.

[0034]FIG. 4 illustrates further processing in which a second mask 34 ispatterned to expose metal upper layer 32 where the exposure issubstantially centered over metallization 14. Second mask 34 isperipherally patterned because a plating process is carried out to platea bump precursor that adheres to metal upper layer 32. FIG. 3 alsoillustrates further processing in which a bump precursor button 36 hasbeen plated over metal upper layer 32 through mask 34. Plating iscarried out by electroless plating techniques or by electroplatingtechniques as is known in the art. By way of non-limiting example,electroplating is carried out to form bump precursor button 36 as adiscrete structure that is spaced-apart from any closest neighboringbump precursors. Accordingly, bump precursor button 36 may have acurvilinear perimeter (not pictured) and a curvilinear vertical profile.Alternatively, a plating film may be formed and subsequently patternedinto substantially discrete bump precursor structures by a process suchas an etch. Accordingly, the bump precursor structure may have arectilinear perimeter (not pictured) and a rectilinear vertical profile(also not pictured). In any event, bump precursor button 34 or apatterned bump precursor structure (not depicted) may be selected from asolder composition that facilitates embodiments.

[0035] It is noted in FIGS. 1-4 that one occurrence of metallization 14has no bump precursor button 36 due to the patterning of mask 34 thathas prevented deposition of solder material. In such an event, themetallization without a bump precursor button may act as a probe sitefor testing or other functions.

[0036] In one embodiment, bump precursor button 36 is a tin-lead solder.In selected embodiments, bump precursor button 36 is a tin-lead soldercomposition such as from Sn97Pb. A tin-lead solder composition that maybe used with a substrate that is to be flip-chip mounted oversemiconductor structure 10 is a Sn37Pb composition. In any event, bumpprecursor button 36 may be a tin-lead solder comprising Sn_(x)Pb_(y),wherein x+y total 1, and wherein x is in a range from about 0.3 to about0.99. Preferably, the bump precursor button 36 is a tin-lead soldercomposition of Sn97Pb, and substrate solder for forming the C4 bond is atin-lead solder composition of Sn37Pb.

[0037]FIG. 5 illustrates further processing in which metal upper layer32 has been removed to expose metal third layer 30 except for the regiondirectly under bump precursor button 36. Metal upper layer 32 is removedby a wet etch as is known in the art. For example, where metal upperlayer 32 is a nitrided NiV material, a wet etch recipe is chosen that isselective to both bump precursor button 36 and to metal third layer 30.One non-limiting example of such a wet etch recipe is a wet sulphonicetch as is known in the art.

[0038]FIG. 6 illustrates further etching in which the three metal layers26, 28, and 30 are removed substantially everywhere except directlyunder bump precursor button 36. Although some undercutting 38 into themetal layers 26-32 beneath bump precursor button 36 may be desirable, itmay be balanced against risking a total slumping of the solder duringreflow. In one embodiment, the etch recipe results in undercutting 38 ofmetal upper layer 32 is about 2.5 microns, undercutting 38 of metalthird layer 30 and metal first layer is about 8 microns each, andundercutting 38 of metal second layer 128 is about 9 microns.

[0039] Etching of metal first layer 26-through metal third layer 30 iscarried out according to various embodiments. In one embodiment, etchinga is carried out in the presence of a nitrogen-containing heterocycliccompound, an ammonium hydroxide compound, an oxidizer, and a metalhalide compound.

[0040] The nitrogen-containing heterocyclic compound is selected frompyrrole, imidazole, oxazole, thizole, pyrazole, 3-pyrroline,pyrrolidine, n-methyl pyrrolidone (NMP) and the like. Other organiccompounds may be used that tend to stabilize the oxidizer. In oneembodiment, a 100% NMP composition is provided in a ratio of about 5volume parts NMP to 2 volume parts ammonium hydroxide compound, to about2 volume parts oxidizer.

[0041] The ammonium hydroxide compound is selected from is selected frommethyl ammonium hydroxide, tetra methyl ammonium hydroxide (TMAH), andthe like. In one embodiment, the ammonium hydroxide compound is 25% TMAHin water that is provided in a ratio of about 2 volume parts to about 5volume parts nitrogen-containing heterocyclic compound, to about 2volume parts oxidizer.

[0042] The oxidizer is selected from ozone, hydrogen peroxide, hydrogenperoxide-containing complexes such as carbamide peroxide (NH₂)₂CO—H₂O₂,and the like. Oxidizers can provide a ready source of active oxygen ineffective concentrations. Oxidizers often have short shelf lives andtherefore it is useful to provide point-of-use oxides that are mixed asthey are to be metered to the etching tool. In one embodiment, theoxidizer is about 30% hydrogen peroxide in water that is provided in aratio of about 2 volume parts hydrogen peroxide to about 5 volume partsnitrogen-containing heterocyclic compound to about 2 volume partsammonium hydroxide compound.

[0043] In all of the etching solution embodiments, a metal halidecompound or the like is provided. In one embodiment, the metal halidecompound is a metal halide salt selected from alkali metal halide saltsand alkaline earth metal halide salts. In one specific embodiment, themetal halide compound is potassium fluoride (KF) in a concentrationrange from about 3 gram/liter to about 5 gram/liter. In one embodimentthe molar concentration of KF is about 0.063 mole/liter. In any event,the molar equivalent concentration in relation to the metal or thehalide is in a range from about 0.05 mole equivalents/liter to about 0.1mole equivalents/liter. Although no specific chemical mechanism is setforth herein for the metal halide compound, the mole equivalentsconcentration may be applicable to either the metal or the halide.

[0044] The following represents non-limiting embodiments of etch recipesaccording to the present invention. During etching, some ofmetallization 14 that is exposed dissolves and presents a potentialcontaminant that can deposit upon passivation layer 20. FIG. 6illustrates a dished area 40, in an arbitrary shape, of metallization 14that is exposed during etching of metal layers 26, 28, and 30. In theseembodiments, etching through metal first layer 26, metal second layer28, and metal third layer 30 is carried out under conditions that retainthe dissolved portion of metallization 14 in an oxidized state such thatit is not redeposited upon passivation layer 20. Some of theseconditions include a pH in a range that is basic. In one embodiment, thepH is maintained in a range from about 7 to about 12. In one embodiment,the pH is maintained in a range from about 9 to about 11.

[0045] In one embodiment, the nitrogen-containing heterocyclic compoundis NMP, the ammonium hydroxide compound is TMAH, the oxidizer ishydrogen peroxide, the metal halide compound is potassium fluoride.Although these specific compounds are set forth, it is understood thatother compound types are included in various embodiments. Given thesecompounds, specifically referred to, but also generically classed as setforth herein, the etching solution the conditions include NMP:TMAH:H₂O₂in a volume ratio that varies the NMP from about 8:5:2 to about 2:5:2.In another embodiment, the etching solution conditions includeNMP:TMAH:H₂O₂ in a volume ratio that varies the TMAH from about 5:6:2 toabout 5:4:2. In another embodiment, the etching solution conditionsinclude NMP:TMAH:H₂O₂ in a volume ratio that, varies the H₂O₂ from about5:5:3 to about 5:5:1. In another embodiment, the etching solutionconditions include NMP:TMAH:H₂O₂ in a volume ratio of about 5:5:2.

[0046] It is noted that for the three variations of volume ratios forthe respective nitrogen-containing heterocyclic-ammonium hydroxide- andoxidizer compounds, combinations of the three variations are embodimentsof the present invention.

[0047] In one embodiment, certain thicknesses of the layers 26-32 areselected. The metal layers should not be too thin individually so thatthe BLM stack is consumed by the migration of tin or the like from thesolder bump precursor button 36. Otherwise, during the temperaturecycling, once the BLM stack is consumed, an intermetallic that forms,segregates and form shapes that may move upward into the solder.Consequently, volume changes that correspond with intermetallicformation may cause significant stress in the electrical structure. Inone embodiment, the metal second layer 28 significantly resistscombination of stack metals with tin in the tin-lead solder.Consequently, where significant consumption of metal upper layer 32 mayoccur, metal second layer 28 acts as a migration stop to tin in thesolder ball that forms from bump precursor button 34.

[0048] The following is a process example that relates to semiconductorstructure 10 as depicted in FIGS. 1-6. A substrate 12 containing an M6metallization and a copper metallization 14 bond pad is provided.Substrate 12 contains a silicon oxide ILD material as is known in theart. A nitride layer 18 and a passivation layer 20 are formed oversubstrate 12 and metallization 14. Passivation layer 20 is a polyimidelayer that is formed according to known technique. Thereafter, aphotoresist first mask (not pictured) is spun on and patterned to exposea recess 22. Etching of passivation layer 20 is carried out in a dryetch. Thereafter, passivation layer 20 is cured such it shrinks invertical dimension, and forms an angle 24 of about 45°. A metal firstlayer 26 is formed by PVD of Ti over substrate 12 and structuressupported thereon. Metal first layer 26 is about 1,000 Å thick in thevertical dimension as depicted in FIG. 3. Next, a metal second layer 28is formed by PVD over metal first layer 26. Metal second layer 28 isaluminum that is about 1,000 Å thick. A metal third layer 30 is formedby PVD of Ti to a thickness of about 1,000 Å. Thereafter, a metal upperlayer 32 is formed by PVD of a NiV alloy over metal third layer 30.Metal upper layer 32 is about 4,000 Å. Nitriding of metal upper layer 32is carried out under thermal processing conditions according to knowntechnique.

[0049] After the formation of the metal layers 26-32, a photoresist mask34 is spun on, cured, exposed, and patterned according to knowntechnique. Patterning of mask 34 exposes metal upper layer 32 directlyabove metallization 14 on one side of the structure depicted in FIG. 4(left), but mask 34 covers an occurrence of metallization 14 on theother side (right). Thereafter, an electroplating solution that has tinand lead in a Sn97Pb proportion is applied over substrate 12 until abump precursor button 36 has been formed. Next, an isotropic wet etch iscarried out that dissolves metal upper layer 32. The wet etch is asulphonic acid or the like according to known technique that isselective to bump precursor button 36.

[0050] After etching of metal upper layer 32, a wet isotropic etch iscarried out that removes first-through third metal layers 26, 28, and 30as set forth herein. Etching temperatures are maintained in a range fromabout 25° C. to about 50° C., and in this example at about 40° C., andan etching time in a range from about 30 seconds to about 20 minutes,and in this example about 10 minutes.

[0051] The wet etch is carried out with a 5:5:2 mixture ofNMP:TMAH:H₂O₂, provided in concentrations as set forth herein, and anabout 3.69 gram/liter amount of KF is added. In this embodiment, the KFis added to TMAH and the H₂O₂ and the NMP are premixed. Thereafter, apoint-of-use mixing is carried out such that the two mixtures are addedas they are metered to a wet etch tool. The temperature of the etch ismaintained at about 40° C. by proper stirring, recirculating etchant,and cooling thereof, and the etch time is about 10 minutes. The pH ofthe etching solution is maintained at about pH 12.

[0052] Thereafter, a thermal process acts that reflows bump precursorbutton 36 to form a solder ball (not pictured).

[0053] In a second example, all processing conditions are similar to theprevious example, except mixing of the KF with the TMAH is the onlypremixture provided. In this example, the H₂O₂ and the NMP are providedseparately and a point-of-use mixing is carried by blending the KF/TMAHmixture and the NMP and H₂O₂ in a three-part point-of-use blending asthe three parts are metered to a wet etch tool.

[0054] In a third example, all processing conditions are similar to theprevious example, except all four components are premixed and metered tothe wet etching tool.

[0055]FIG. 7 is a process flow diagram of an embodiment. The process 700includes forming 710 a metal first layer over a metallization as setforth herein. Processing continues by forming 720 a metal second layerover the metal first layer. According to one embodiment, a metal thirdlayer is formed 730 over the second metal layer, and the metal thirdlayer is the same metal or type as the metal first layer. In any event,a metal upper layer is formed 740 over the metal second layer, eitherabove and on it, or above and on the metal third layer. An electricallyconductive bump is formed 750 as set forth herein. Thereafter etching760 of the BLM stack is carried out as set forth herein. In particular,a first wet etch is carried out that removes the metal upper layereverywhere except under the bump precursor button. A second wet etch isnext carried out that removes the metal first- through metal thirdlayers. Process control is used to maintain etch temperature, pH, andthe oxidation conditions in order to prevent redeposition of anymetallization onto the passivation layer or other structures.

[0056] According to the details set forth herein, an embodiment of thepresent invention relates to a BLM etching system. The BLM etchingsystem includes a substrate including a metallization pad. The systemalso includes a BLM stack and a bump precursor button as set forthherein. The system also includes an etch recipe as set forth herein. Ina specific embodiment, the BLM etching system includes NMP, TMAH, H₂O₂,and KF.

[0057] Additionally, according to details set forth herein, anembodiment of the present invention relates to a BLM etching solutionincluding a nitrogen-containing heterocyclic compound, an ammoniumhydroxide compound, an oxidizer, and a metal halide compound, whereinthe solution has a pH greater than or equal to about 7.

[0058] It will be readily understood to those skilled in the art thatvarious other changes in the details, material, and arrangements of theparts and method stages which have been described and illustrated inorder to explain the nature of this invention may be made withoutdeparting from the principles and scope of the invention as expressed inthe subjoined claims.

1-14. (Canceled)
 15. A ball-limiting metallurgy (BLM) etching system comprising: a substrate including a metallization pad; a BLM stack including: a metal first layer disposed above and on the metallization pad; a metal second layer disposed above and on the metal first layer; a metal upper layer disposed above the metal second layer; an electrically conductive bump disposed above and on the BLM stack; and an etch recipe that includes: n-methyl pyrrolidone(NMP), tetra methyl ammonium hydroxide (TMAH), hydrogen peroxide (H₂O₂), and potassium fluoride (KF); and etching conditions that resist dissolving the electrically conductive bump.
 16. The BLM etching system according to claim 15, wherein the etching conditions include NMP:TMAH:H₂O₂ in volume ratio ranges from about 8:5:2 to about 2:5:1, from about 5:6:2 to about 5:4:2, and from about 5:5:3 to about 5:5:1.
 17. The BLM etching system according to claim 15, wherein the etching conditions include KF in a range from about 3 g/liter to about 5 g/liter.
 18. The BLM etching system according to claim 15, wherein the etching conditions include an etching temperature in a range from about 25° C. to about 50° C.
 19. The BLM etching system according to claim 15, wherein the etching conditions include an etch time in a range from about 30 seconds to about 20 minutes.
 20. The BLM etching system according to claim 15, wherein the refractory metal upper layer is selected from a refractory metal, metal-doped refractory metal, or a refractory metal alloy selected from Ni, Co, Pd, Pt, NiV, CoV, PdV, PtV, Ti, Zr, Hf, Cr, Mo, W, Sc, Y, La, and Ce in a solid-solution or stoichiometric ratio.
 21. The BLM etching system according to claim 15, wherein the electrically conductive bump comprises a tin-lead solder composition selected from Sn37Pb, Sn97Pb, and Sn_(x)Pb_(y), wherein x+y total 1 and wherein x is in a range from about 0.3 to about 0.99.
 22. The BLM etching system according to claim 15, further comprising: a metal third layer disposed above and on the metal second layer, wherein the metal third layer is substantially the same metal as the metal first layer.
 23. A ball-limiting metallurgy (BLM) etching system comprising a solution including a nitrogen-containing heterocyclic compound, an ammonium hydroxide compound, an oxidizer, and a metal halide compound, wherein the solution has a pH greater than or equal to about
 7. 24. The BLM etching system according to claim 23, wherein the heterocyclic compound includes n-methyl pyrrolidone, wherein the ammonium hydroxide compound includes tetra methyl ammonium hydroxide, wherein the oxidizer includes hydrogen peroxide, and wherein the metal halide compound includes potassium fluoride.
 25. The BLM etching system according to claim 23, wherein the heterocyclic compound includes about five volume parts n-methyl pyrrolidone; wherein the ammonium hydroxide compound includes about two volume parts 25% tetra methyl ammonium hydroxide in water; wherein the oxidizer includes about two volume parts 30% hydrogen peroxide in water; and wherein the metal halide compound includes about 4 gram/liter potassium fluoride in the solution.
 26. The BLM etching system according to claim 23, wherein the solution is provided in two parts including: a first part containing the heterocyclic compound and the oxidizer; and a second part containing the ammonium hydroxide compound and the metal halide compound.
 27. The BLM etching system according to claim 23, wherein the solution is provided in three parts including: a first part containing the heterocyclic compound; a second part containing the ammonium hydroxide compound and the metal halide compound; and a third part containing the oxidizer. 